The latest debate initiated recently by Trump is regarding the interpretation of 14th Amendment. "...and subject to the jurisdiction thereof"

What

"...So what was to be the premise behind America’s first and only constitutional birthright declaration in the year 1866? Simply all children born to parents who owed no foreign allegiance were to be citizens of the United States – that is to say – not only must a child be born but born within the complete allegiance of the United States politically and not merely within its limits.

...Under Sec. 1992 of U.S. Revised Statutes the same Congress who had adopted the Fourteenth Amendment, confirmed this principle: “All persons born in the United States and not subject to any foreign power, excluding Indians not taxed, are declared to be citizens of the United States.”

...Who are the subjects of a foreign power? Thomas Jefferson said “Aliens are the subjects of a foreign power.” Thus, the statute can be read as “All persons born in the United States who are not aliens, excluding Indians not taxed, are declared to be citizens of the United States.”

...This remark by Sen. Howard places this earlier comment of his on who is “subject to the jurisdiction thereof” into proper context: “This will not, of course, include persons born in the United States who are foreigners, aliens, who belong to the families of ambassadors or foreign ministers accredited to the Government of the United States, but will include every other class of persons.”

According to this debate, I summarize: if a child is born of an "alien" meaning a citizen of another country, that is NOT a legal citizen of our country, then the child does not automatically become a citizen of our country. I am just going according to the study in the above article/link.

This is already law, but the Supremes make their own decisions on what is law and what is not law.
On the other hand, illegal aliens are not considered protected by our laws and therefore not "subject to the jurisdiction.." A good argument could be made that the 14th Amendment does not automatically make the child a citizen of the U.S. I do realize that all this is dependent on a liberal interpretation of the supreme court.